Dimmer lighting and control systems are widely used in indoor lighting to provide a softer feel and more controllable illumination experience as compared to on/off lighting. Prior dimmer lighting systems have employed dimmer switch controls that include an on/off switch and an up/down power control, master unit and remote units, and microprocessor control for various power-up, power-down and fade in/out functions. Rather than use a variable resistor type rheostat which wastes power and generates heat at low illumination levels, modern dimming systems employ phase regulation, in which the power circuit is switched on at a time delay following a zero-crossing of the AC sine wave input until the end of each half cycle in order to supply a variable level of power to the lighting load.
However, prior multi-location dimmer control systems have various shortcomings and problems in operation. In systems that employ master and remote units, the remote units are “dumb” boxes that simply have on/off and up/down switches but do not indicate the lighting status of the system. Attempts to provide two-way communication functions between the master and remote units would impose added costs and difficulties in outfitting the remote units with power sources and the capability to communicate with the master unit.
For example, a typical prior art multi-location dimmer (shown in FIG. 5) consists of a fully functional master unit and a number of remote units (1, . . . n), where the remote units are connected in parallel with each other between a “switched hot” line of the master unit and a “Traveler” or “Control” line of the master unit. The remote units communicate to the master unit by sending a portion of the output current on the Traveler line to the control input of the master unit. To transmit three commands (Up, Down, and Toggle On/Off), positive, negative and alternating waveforms are used. These remote units require no power in normal operation, and cannot display the level of light setting. To display the light setting level, the remote units would require power and two-way communication means. The task of supplying power to the remote units is quite complicated, as every remote would need some current to operate. With the remote units connected in parallel, total current drawn from the control terminal of the master unit unit would be proportional to the number of remote units connected to the system. When this current reaches a certain level, the lamp load may start glowing (showing illumination) when it is supposed to be in the Off condition. Also the power supply size needed would increase in proportion to the maximum number of remote units that could be connected to the system.
For a multi-location dimmer that supplies power to the remote units, there may be a problem that the internal dimmer's power supply could create an audible noise in the load when the load is Off, which otherwise would be masked when the load is On. This power supply may also generate waste heat.
It is also known in prior dimmer control systems to use control memory to restore the illumination level to the same level as when it was last powered off, as a user often sets the illumination level to a desired comfort level and wants the same level when turning the light system back on again. However, the use of a separate latch device is limited to memorizing only whether the load was on or off, and the use of ongoing memory storage of the current power level requires use of a memory component capable of extremely high usage of read/write cycles, which imposes an added cost.